Adjusting and maintaining a person's body temperature using external means has proven to be a difficult task in many instances. One means of adjusting and maintaining body temperatures is to submerge the patient into a bath of water. The water temperature in the bath is chosen to properly adjust the patient's temperature. Although this technique has proven to be quite useful in many applications it is not particularly appropriate in many instances.
For example, this approach often does not fare well with hypothermia patients. In such cases, the patient is typically submerged in a very warm bath to raise the body temperature of the patient. The use of a water bath is, however, frequently impractical, for it requires the use of a bath tub of sufficient size to completely submerge a patient, and it also requires close regulation of water temperature. Furthermore, this approach is time consuming because time must be spent preparing the warm bath. In cases such as at sea when a person has fallen overboard, these impracticalities can prove to be quite costly.
Another situation where the use of a water bath is impractical for regulating body temperature is in a clinical environment, including a surgical environment. Operating rooms are most often maintained at fairly cold temperatures to aid in the comfort of the surgical personnel. Unfortunately, it is not typically desirable for the patient to be exposed to such cool temperatures. In colder temperatures, patients tend to bleed more profusely and many patients may become uncomfortably chilled by the cold.
Patient warming approaches which have been used in clinical environments, but which are not usually practical in surgery, include warm air blanket systems and water blankets. Blankets filled with warm water suffer poor overall heat transfer in view of a failure to contact low points in the body contours. Further, due to compression of the water blanket against heated areas, blood flow from those heated areas may be limited and local tissue damage may result. With warm air systems, warm air flows through holes from an inflated blanket toward the patient. With the air flowing directly against the patient, uniform heat distribution to the patient's skin is assured. However, the warm air presents a relatively low heat transfer coefficient.
With the poor heat transfer of the air and water blankets and with the requirement that temperature be held sufficiently low to prevent tissue damage, it is necessary that the blankets cover large surface areas. As a result, they become cumbersome and expensive. Further, by warming such a large surface area of the skin, vasodilation in that large area can result in a significant and undesirable redistribution of the blood flow in the body.